A line-of-sight direction determining apparatus for determining the direction of a person's line of sight needs to represent a detected direction in coordinates in external space.
Patent literature 1 discloses a line-of-sight detecting apparatus that detects in advance the condition of the eyeball while looking at a specific direction and determines from that result whether or not the eyeball is looking at a specific direction. The apparatus disclosed in patent literature 1 attentively views an indicator in a finder and corrects the difference between the visual axis and the eye axis then.
Patent literature 2 discloses a driving condition detecting apparatus that observes the direction of a driver's line of sight over a long period of time during driving, and from its distribution determines a reference line-of-sight direction. The apparatus disclosed in patent literature 2 estimates a reference line-of-sight position from time series data.
Thus, conventionally, there are two categories of methods of line-of-sight direction determination. One is to specify or detect a target to attentively view and detect the condition of attentive viewing (e.g. apparatus disclosed in patent literature 1), and the other one is to determine the center of the direction of line of sight from the distribution of line of sight over a long period of time (e.g. apparatus disclosed in patent literature 2).